In recent years, there has been an increasing tendency toward use by the military services of armored personnel carriers to transport infantry and helicopter gun ships, which are also armored to shoot at infantry. With this increasing use of armor, the rifle bullets of the relatively recent past are, in many cases, rendered relatively ineffective due to their inability to effectively penetrate light armor. Two recent small caliber ammunition (.50 caliber and under) developments have changed the situation somewhat. The first is the reintroduction of the steel nosed lead bullet in such forms as the new NATO 5.56 mm round (called the "M855 by the U.S. Army). The second is the development by Winchester (Olin Corporation) of the first truly effective 7.62 mm and .50 Caliber (12.7 mm) Saboted Light Armor Penetrating rounds. The new Olin SLAP rounds have proven extremely effective while the somewhat rounds have proven extremely effective while the somewhat more inexpensive NATO round has proven to be a significant improvement over the prior 5.56 mm ball round. It would seem that little further could be done to improve the 5.56 mm round, since 5.56 mm is too small to reduce its caliber further to give a saboted round, except perhaps to single flechette, and as yet flechette rifle rounds have all been abandoned as unseccessful.
However, when Winchester attempted to duplicate the M855 round, some unexpected results occured. The Winchester version consistently outperformed the NATO round. In view of this, further experimentation was done to determine the cause of these unexpected results so that the improvements could be introduced into the round. It will be understood that since the M855 round is designed to penetrate armor, the more armor the round can penetrate the better. Thus, surprisingly, a heretofor unrecognized problem was discovered in the existing round and the penetration ability of the round greatly improved.
The improved penetration ability is achieved by the present invention which provides for case hardened steel noses for the round, the hardness of the nose being Rockwell C50 minimum at a depth of 0.030 inches, with the interior of the nose being below Rockwell C50in hardness.